1. Field of the Invention
The present invention relates generally to internal combustion engines and, more particularly, to an internal combustion engine having a stratified charge combustion chamber in which combustion is initiated by the ignition of a rich air-fuel mixture which in turn initiates ignition of a lean air-fuel mixture.
2. Description of the Prior Art
As a result of increasingly stringent governmental regulations regarding the content of exhaust gases emitted from internal combustion engines, various efforts are being made to control the amount of noxious components in engine emission and to improve fuel economy. Several different approaches to the solution of this problem are currently being investigated. One approach is to treat gases exhausted from an internal combustion engine by a catalytic converter or other device before the gases are released to the atmosphere. Another approach is to construct an internal combustion engine that will initially produce exhaust gases having a relatively low content of noxious components.
Recently, interest has increased in building internal combustion engines that utilize the charge stratification technique to reduce the contamination in engine exhaust gases. Charge stratification systems operate on the principle that the combustion of lean fuel mixtures produces lower emissions and good fuel economy. In a stratified charge internal combustion engine, the central principle is to supply a rich air-fuel mixture near the point of ignition inside the cylinder while the rest of the mixture in the combustion chamber is kept lean. For example, it is known to provide a four stroke cycle internal combustion engine with a main combustion chamber which contains a lean air-fuel mixture and an auxiliary or precombustion chamber connected with the main chamber by a restricted passage or orifice which contains a rich air-fuel mixture. The rich air-fuel mixture is supplied to this precombustion chamber through an additional intake valve while the lean air-fuel mixture is supplied to the main combustion chamber through the normal intake valve. In this engine combustion originates in the precombustion chamber and a jet of burning gases is then forced into the main combustion chamber. These burning gases ignite the lean mixture in the main combustion chamber thereby permitting the internal combustion engine to burn leaner fuel mixtures. Examples of such stratified charge internal combustion engines using a precombustion chamber in communication with a main combustion chamber are shown in several patents such as U.S. Pat. No. 3,941,105 issued to Yagi et al; U.S. Pat. No. 3,830,205 issued to Date et al; and U.S. Pat. No. 3,924,592 issued to Miyaki et al. The above patents generally describe the compound vortex controlled combustion engine (CVCC) manufactured by Honda Giken Kogyo Kabushiki Kaisha.
Although the above stratified charge internal combustion engines improve fuel economy and reduce pollutants, several disadvantages result therefrom. The addition of a fixed precombustion chamber increases the overall surface area of the combustion chamber. This results in an increase in the area subject to cooling which increases the likelihood of boundary layer quenching during the combustion process. Furthermore, the amount of control over the stratification of the charge in the combustion chamber is limited because the vortex or orifice between the precombustion chamber and the main combustion chamber always permits some degree of communication between the chambers. Also, in known stratified charge internal combustion engines the precombustion chamber must be limited in size in order to achieve sufficient compression of the air-fuel mixture in the precombustion chamber. This lack of control over the compression in the precombustion chamber decreases the efficiency of the combustion process and, because of this size limitation, the precombustion chamber has a large surface area per unit volume which increases the boundary layer problems mentioned above.
Several prior art attempts have been made to overcome the above disadvantages. For example, U.S. Pat. No. 3,929,107 issued to Renger and U.S. Pat. No. 4,011,841 issued to Sato et al show stratified charge internal combustion engines in which a homogeneous air-fuel mixture in a primary combustion chamber and a precombustion chamber is separately compressed and ignited. In these patents, an auxiliary piston mounted on the primary piston separately compresses the air-fuel mixture in the precombustion chamber. As a result, the compression in the precombustion chamber can be more precisely controlled during the compression stroke of the primary reciprocating piston. Although the auxiliary piston provides control over the compression in the precombustion chamber, at the point of ignition of the air-fuel mixture in the precombustion chamber there is no communication with the main combustion chamber and, as a result, part of the combustion process takes place solely in the precombustion chamber. Also, it is difficult in these systems to provide proper sealing between the auxiliary piston and the walls of the precombustion chamber. Finally, because these systems also use a separate precombustion chamber adjacent the main combustion chamber, the overall surface area of the combustion chamber is increased which results in the boundary layer problems mentioned above.
Another United States patent which shows a stratified charge internal combustion engine having an auxiliary piston for controlling the compression in the precombustion chamber is U.S. Pat. No. 3,777,724 issued to Kiley. The engine disclosed in the Kiley patent does not use a homogenous air-fuel mixture but rather uses a combination of rich and lean mixtures as generally known. In the Kiley patent, an auxiliary piston or volume control member mounted on the primary piston projects into and varies the volume of the precombustion chamber to maintain a constant predetermined ratio between the volumes of the main and precombustion chambers during a portion of the reciprocating movement of the primary piston. Again, although this auxiliary piston controls the compression in the precombustion chambers, it does not overcome the other disadvantages of known stratified charge internal combustion engines mentioned above.